The invention relates to a process for successive grinding of crankpins of a crankshaft by means of a grinding attachment, for example a rotating wheel, in which process the crankshaft is clamped at two spaced center journals and is rotated around the axis of the crankpin to be ground, and to a grinder especially for implementing such process.
In a known process for grinding crankpins, the two outermost center or main bearing journals of the crankshaft are clamped eccentrically in chucks of work headstocks and the crankpins are ground in succession by a grinding wheel. In such grinding operations, the bending behavior of the crankshaft clamped only at its two ends is problematic when the crankshaft exceeds a specific length and/or a specific weight. The consequence of deflection of the crankshaft resulting from its own weight is an elastic deformation in the region of the crankpins to be ground, such deflection not allowing required tolerances for concentricity and width to be maintained. Also, the piston stroke length required for optimal combustion in the cylinder cannot be reached in these cases with crankpins that are ground inaccurately. To reduce dimensional deviations as a consequence of deflection, the crankpin to be ground is braced in the known method while grinding by means of a separate steady rest, which absorbs a part of the weight of the workpiece. Such steady rests are, however, time-consuming to mount and can compensate only partially for the deflection of the shaft. In particular, during mass production, grinding the crankpins of the crankshafts is done in succession on several different grinders, whereby only the crankpin immediately adjacent internally to the center journal intended for clamping is ground. Grinding is done simultaneously with two wheels beginning with the two outermost crankpins directly next to the clamping points. The next two crankpins that follow inwardly have to be ground on another machine, whereby the crankshaft is clamped on the center journals directly adjacent outwardly to the crankpins to be ground, etc. A work headstock is not necessary, since the chucks acting directly next to the crankpin to be ground guarantees adequate bracing. In such a process, three double wheel grinders alone are necessary, for example, for the production of a six-throw crankshaft. This can be justified for mass production operations, but for operations involving smaller quantities it is not profitable.